Empirical and computational study on conservative tracer migration through a single fracture

The escalation of industrialization and population growth in recent decades has increased the prominence of groundwater pollution in environmental concerns. However, accurate prediction of the contaminant migration through the fractured aquifer is still an arduous task. The current research is dedicated to evaluating the predictive accuracy of three models: the Advection Dispersion Equation (ADE), Advection Dispersion Equation with Retardation (ADE-R), and Single Rate Mobile-Immobile (MIM) model. Constant dispersivity is assumed for all the models. These models were employed to predict the migration of the solute, particularly NaCl, within a single fracture characterized by a 0.3 cm aperture and 1000 cm length and filled with fine sand. The study maintained non-Darcian flow conditions throughout the experimental runs. The simulated BTCs exhibited a non-Fickian trend and were subsequently subjected to fitting using the ADE, ADE-R, and MIM models. Notably, the MIM model proved the most adept at fitting the simulated BTCs, effectively capturing both early arrival and long tails. Conversely, the ADE-R model excelled in predicting the early arrival but fell short in fitting the long tails of the BTCs.

Keywords: ADE model; ADE-R model; Breakthrough curves; filled-single fracture; MIM model; non-Darcian flow